The present invention relates to isolated polynucleotide sequences exhibiting endothelial cell specific promoter activity, and methods of use thereof and, more particularly, to a modified-preproendothelin-1 (PPE-1) promoter which exhibits increased activity and specificity in endothelial cells. The invention further relates to modifications of the PPE promoter, which enhance its expression in response to physiological conditions including hypoxia and angiogenesis.
Angiogenesis, the process of formation of new blood vessels, plays an important role in physiological processes such as embryonic and postnatal development as well as in wound repair. Formation of blood vessels can also be induced by pathological processes involving inflammation (e.g., diabetic retinopathy and arthritis) or neoplasia (e.g., cancer) (Folkman, 1985, Perspect, Biol. Med., 29, 10).
Angiogenesis occurs under conditions of low oxygen concentration (ischemia and tumor metastases etc.) and thus may be an important environmental factor in neovascularization. The expression of several genes including erythropoietin, transferrin and its receptor, most of glucose transport and glycolytic pathway genes, LDH, PDGF-BB, endothelin-1 (ET-1), VEGF and VEGF receptors is induced under hypoxic conditions by the specific binding of the Hypoxia Inducible Factor (HIF-1) to the Hypoxic Response Element (HRE) regulating the transcription of these genes. Expression of these genes in response to hypoxic conditions enables the cell to function under low oxygen conditions.
The angiogenic process is regulated by angiogenic growth factors secreted by tumor or normal cells as well as the composition of the extracellular matrix and by the activity of endothelial enzymes (Nicosia and Ottinetti, 1990, Lab. Invest., 63, 115). During the initial stages of angiogenesis, endothelial cell sprouts appear through gaps in the basement membrane of pre-existing blood vessels (Nicosia and Ottinetti, 1990, supra; Schoefl, 1963, Virehous Arch, Pathol. Anat. 337, 97-141; Ausprunk and Folkman, 1977, Microvasc. Res. 14, 53-65; Paku and Paweletz, 1991, Lab. Invest. 63, 334-346). As new vessels form, their basement membrane undergoes complex structural and compositional changes that are believed to affect the angiogenic response (Nicosia, et. al., 1994, Exp Biology. 164, 197-206).
Unbalanced angiogenesis typifies various pathological conditions and often sustains progression of the pathological state. For example, in solid tumors, vascular endothelial cells divide about 35 times more rapidly than those in normal tissues (Denekamp and Hobson, 1982 Br. J. Cancer 46:711-20). Such abnormal proliferation is necessary for tumor growth and metastasis (Folkman, 1986 Cancer Res. 46:467-73).
Vascular endothelial cell proliferation is also important in chronic inflammatory diseases such as rheumatoid arthritis, psoriasis and synovitis, where these cells proliferate in response to growth factors released within the inflammatory site (Brown & Weiss, 1988, Ann. Rheum. Dis. 47:881-5).
In atherosclerosis, formation of an atherosclerotic plaque is triggered by a monoclonal expansion of endothelial cells in blood vessels (Alpern-Elran 1989, J. Neurosurg. 70:942-5). Furthermore, in diabetic retinopathy, blindness is thought to be caused by basement membrane changes in the eye, which stimulate uncontrolled angiogenesis and consumption of the retina (West and Kumar, 1988, Lancet 1:715-6).
Endothelial cells are also involved in graft rejection. In allograft rejection episodes, endothelial cells express pro-adhesive determinants that direct leukocyte traffic to the site of the graft. It is believed that the induction of leukocyte adhesion molecules on the endothelial cells in the graft may be induced by locally-released cytokines, as is known to occur in an inflammatory lesion.
Abrogated angiogenesis, on the other hand, is also a major factor in disease development, such as in atherosclerosis induced coronary artery blockage (e.g., angina pectoris), in necrotic damage following accidental injury or surgery, or in gastrointestinal lesions such as ulcers.
Hence, regulating or modifying the angiogenic process can have an important therapeutic role in limiting the contributions of this process to pathological progression of an underlying disease state as well as providing a valuable means of studying their etiology.
Recently a significant progress in the development of endothelial regulating agents, whether designed to be inhibitory or stimulatory, has been made. For example, administration of aFGF protein, within a collagen-coated matrix, placed in the peritoneal cavity of adult rats, resulted in a well vascularized and normally perfused structure (Thompson, et al., PNAS 86:7928-7932, 1989). Injection of βFGF protein into adult canine coronary arteries during coronary occlusion reportedly led to decreased myocardial dysfunction, smaller myocardial infarctions, and increased vascularity (Yanagisawa-Miwa, et al., Science 257:1401-1403, 1992). Similar results have been reported in animal models of myocardial ischemia using βFGF protein (Harada, et al., J Clin Invest 94:623-630, 1994, Unger, et al., Am J Physiol 266:H1588-H1595, 1994).
However, for mass formation of long lasting functional blood vessel there is a need for repeated or long term delivery of the above described protein factors, thus limiting their use in clinical settings. Furthermore, in addition to the high costs associated with the production of angiogenesis-regulating factors, efficient delivery of these factors requires the use of catheters to be placed in the coronary arteries, which further increases the expense and difficulty of treatment.
With the identification of new genes that regulate the angiogenic process, somatic gene therapy has been attempted to overcome these limitations. Although, great efforts have been directed towards developing methods for gene therapy of cancer, cardiovascular and peripheral vascular diseases, there is still major obstacles to effective and specific gene delivery. In general, the main limiting factor of gene therapy with a gene of interest using a recombinant viral vector as a shuttle is the ability to specifically direct the gene of interest to the target tissue. Indeed, non-specific gene targeting, results in systemic expression of the transgene which leads to several problems. For example, systemic expression of VEGF, a key regulator of the angiogenic process has been tested in animal models of ischemia and in clinical trials [Hammond, H. K. and McKirnan, M. D. Cardiovasc Res 49, 561-7. (2001); Gowdak, L. H. et al. Circulation 102, 565-71. (2000); Rosengart, T. K. et al. Ann. Surg. 230, 466-70; discussion 470-2. (1999). Simovic, D et al. Arch Neurol 58, 761-8. (2001)]. However, due to the systemic nature of expression, all modalities of treatment faced the problems of facilitated atherogenesis [Dulak J. (2001) J Am Coll Cardiol 38:2137-8 and Celletti F L et al. (2001) J Am Coll Cardiol 2126-30] and edema [Harrigan M R et al. (2002) Neurosurgery 50:589-598; Funatsu H et al. (2002) Am J Opthalmol 133:70-7; Thicket D R (2001) Am J Respir Crit. Care Med 164:1601-5], vessel immaturity, hyper permeability and regression [Benjamin, L. E et al (1999) J Clin Invest 103:159-65; Alon, T et al. Nat Med 1:1024-8. (1995); Benjamin, L. E. et al. (1997) Proc Natl Acad Sci USA 94:8761-6].
Hence, regulation of the angiogenic process by targeted gene therapy to the vascular endothelium can be tremendously important in inducing efficient therapy for these diseases.
Several endothelial cell specific promoters have been described in the prior art. For example, Aird et al., [Proc. Natl. Acad. Sci. (1995) 92:7567-571] isolated 5′ and 3′ regulatory sequences of human von Willebrand factor gene that may confer tissue specific expression in-vivo. However, these sequences could mediate only a heterogeneous pattern of reporter transgene expression. Bacterial LacZ reporter gene placed under the regulation of von Willebrand regulatory elements in transgenic mice revealed transgene expression in a subpopulation of endothelial cells in the yolk sac and adult brain. However, no expression was detected in the vascular beds of the spleen, lung, liver, kidney, heart, testes and aorta as well as in the thrombomodulin locus.
Korhonen J et al [Blood (1995) 96:1828-35] isolated the human and mouse TIE gene promoter which contributed to a homogeneous expression of a transgene throughout the vascular system of mouse embryos. However, expression in adult was limited to the vessels of the lung and kidney and no expression was detected in the heart, brain, liver. Similar results were obtained by Schlaeger M et al. who isolated a 1.2 kb 5′ flanking region of the TIE-2 promoter, and showed transgene expression limited to endothelial cells of embryonic mice [Schlaeger T M et al. (1995) Development 121:1089-1098].
Thus, none of these sequences work uniformly in all endothelial cells of all developmental stages or in the adult animal. Furthermore, some of these sequences were not restricted to the endothelium.
U.S. Pat. No. 5,747,340 teaches use of the murine PPE-1 promoter and portions thereof. However, this patent contains no hint or suggestion that an endothelial-specific enhancer can be employed to increase the level of expression achieved with the PPE promoter while preserving endothelial specificity. Further, this patent does not teach that the PPE-1 promoter is induced to higher levels of transcription under hypoxic conditions.
An autonomous endothelial-specific enhancer in the first intron of the mouse TIE-2 gene was recently described. Combination of the TIE-2 promoter with an intron fragment containing this enhancer allowed it to target reporter gene expression specifically and uniformly to all vascular endothelial cells throughout embryogenesis and adulthood [Schlaeger T M (1997) Proc. Natl. Acad. Sci. 94:3058-3063]. Though, promising until today no expression of angiogenic transgenes have been described in conjugation with this regulatory element.
While reducing the present invention to practice, the present inventors have constructed and employed a novel configuration of the PPE-1 promoter which exhibits unexpected and highly specific activity in endothelial cells participating in angiogenesis.
Due to its capability to direct high expression of exogenous genes in an endothelial cell specific manner, the PPE-1 promoter of the present invention, which is designated as PPE-1-3X herein, enables regulating endothelial-specific processes. Thus, angiogenesis-regulating factors placed under the modified promoters of the present invention can serve as powerful in-vivo pro-angiogenic or anti-angiogenic tools in basic research and in clinical applications, such as of the cardiovascular system.